In many medical applications there is a need for a wrapping or covering material that is resistant to penetration of fluids containing bacterial contamination, but is also permeable to gases. Gas permeability is desirable, for example, to permit the infusion of a gas such as steam or ethylene oxide for sterilization, or to permit the passage of air and water vapor when the material is used as a drape for covering patients or for making surgical gowns. There is also a need for liquid-impermeable, gas-permeable materials for nonmedical applications such as protective clothing.
In designing such a material, it is difficult to prevent the penetration of liquids without making the material insufficiently permeable to air. Various methods involving the use of a water-repellent surface treatment or lamination of several layers have been proposed to achieve the desired combination of properties. A water-impervious, gas-permeable laminated material comprising a ply of hydrophobic, microfine fibers produced by a dry forming, melt blown process, fuse-bonded to a layer of conjugate fibers having a low melting sheath and a high melting core is described in U.S. Pat. No. 4,657,804 (Mays et al.). This material is impregnated with a water-repellent binder and treated with a water-repellent finish. U.S. Pat. No. 4,196,245 (Kilson et al.) discloses a composite nonwoven fabric comprising at least two adjacent hydrophobic plies of microfine fibers produced by a dry forming, melt blown process, and one air-permeable, nonwoven cover ply. GB 2,095,616 describes a liquid-impermeable, water vapor-permeable material comprising a layer of absorbent nonwoven fabric that is free of any surface-active component and a layer of water-repellent nonwoven fabric, which may be treated with a water-repellent finish. The layers are attached to one another by means of a discontinuous layer of hydrophobic material.
A material that can be produced by a wet forming process and provide resistance to penetration of liquids containing bacterial contamination and that is also gas-permeable, without requiring a water-repellent surface treatment or lamination to other materials, would be an improvement over presently available materials.